1. Field of the Invention
The present invention relates to evaporators for use in chemical analysis. More particularly, the present invention relates to solvent evaporators and dryers used in conjunction with procedures involving sugar analysis of biological materials.
2. Discussion of Background
Many laboratory applications require evaporation of a solvent, either completely or partially, from a sample solution. In particular, sugar analysis of biological materials involving gas chromatography by itself or in conjunction with mass spectrometry includes the alditol acetate procedure. As a result of this procedure, borate are formed in the sample solution that must be evaporated before analysis of the sample can proceed.
In the ordinary alditol acetate procedure, free sugars are reduced with sodium borohydride followed by acetylation with acetic anhydride, which makes the sugars volatile. However, borate generated from the sugar reduction step complexes with hydroxyl groups of sugars thereby inhibiting the subsequent acetylation step.
The borate must be evaporated before the acetylation step. Currently, evaporation involves five cycles of adding manually 2.5 ml of methanol/acetic acid to each sample followed by evaporation under nitrogen to dryness. This manual process is extremely time consuming and requires constant attendance. Thus, an automated evaporation device for this purpose is most desirable.
Evaporators, including automated evaporators, have been known since the 1960s. None of the known evaporators are of the appropriate configuration and sufficiently practical to meet the evaporation needs of procedures such as the one described herein, that is, wherein a solvent is repeatedly added to and subsequently evaporated from a plurality of samples.
In U.S. Pat. No. 5,100,623, Friswell discloses an evaporation apparatus having a matrix of sample vessels held in a temperature-controlled water bath, each vessel being provided with nozzles for supplying gas and liquid. Pressurized air is flowed from the nozzles into the vessels to evaporate the solvent. A system of light detecting sensors and solenoid valves are used to control solvent addition to and evaporation from individual sample vessels.
Newhouse et al. (U.S. Pat. No. 4,604,363) describe an automatic, evaporator system performing evaporation and concentration, combined with solvent exchange, for a variety of different types of samples in sequence. In this system, slugs of sample solutions are delivered to a temperature- and pressure-controlled evaporation chamber. In operation, each slug is evaporated before the next is delivered. The process is repeated until the desired sample volume is attained.
Another evaporating device is described in U.S. Pat. No. 5,039,614, in which Dekmezian et al. disclose a carousel-type fraction collector for use in a method and apparatus for collecting samples for analysis of chemical composition. The collector has a plurality of plates or hollowed dishes formed of potassium bromide and placed in a vacuum oven. Effluent from a fractionator unit, such as a gel permeation chromatograph, is supplied to each plate in turn in the form of droplets. As a droplet falls onto a plate, the solvent is immediately flashed off leaving behind a solid residue. When the desired number of droplets has been deposited on the plate, a stepper motor rotates the carousel to the next collector position. After sample collection is complete, the carousel is removed from the oven and the samples are analyzed by a suitable microanalytical technique.
In an another U.S. Pat. No. (4,820,044), Crighton et al disclose a transport detector system having an elute delivery tube, a plurality of moveable spokes projecting radially from a circular hub, one or more evaporators, a detector, one or more coolers, and a stepper motor. In operation, as the hub is rotated in discrete steps, each spoke passes beneath the tube and droplets of the elute are deposited on each spoke in turn. The spokes then pass through the evaporators, the detector, and the coolers. Evaporators used in this process include hot air blowers at temperatures between 20.degree. C. and 300.degree. C.
Them is a need for a simple and cost-effective evaporator that is suitable for unattended, multi-cycle evaporation procedures involving multiple samples, such as the evaporation requirements of the alditol acetate procedure used in sugar analysis of biological materials.